Blade outer seal assembly

ABSTRACT

An outer seal assembly of a turbine rotor stage is secured within a circumferential groove of the turbine casing in such a manner as to both fix the outer seal assembly in its installed position and also provide for sealing around its outer periphery so as to thereby prevent the leakage of cooling air therearound. A plurality of arcuate elements having an angle-shaped cross sectional profile are provided to interface between radially extending arms of the outer seal assembly and the inner surface of the casing, with a locking mechanism then being applied to secure the two structures in their installed positions. Each of the arcuate elements includes a radially extending panel, a plurality of forwardly extending hooks that are disposed within a groove in the casing, and a second forwardly extending flange that engages the rear surface of the outer seal assembly arm. As the outer seal assembly arm is urged rearwardly during operation, the arcuate element is caused to rotate about a fulcrum in the circumferential groove such that a radially outer edge of the radially extending panel is urged against a casing inner surface so as to thereby enhance the sealing relationship therebetween.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.: (DocketNo.: 965_(—)015, entitled “Split Ring Retainer for Turbine Outer AirSeal) filed concurrently herewith and incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

The United States Government has certain rights in this inventionpursuant to contract number N00019-02-C-3003 between the United StatesNavy and United Technologies Corporation.

FIELD OF THE INVENTION

The invention relates generally to jet engines and, more particularly toa blade outer air seal assembly for use in the turbine section of a jetengine.

BACKGROUND OF THE INVENTION

In a jet engine, wherein a turbine rotor is mounted for rotation withinan engine casing, it is common to provide a blade outer air seal (BOAS)between the casing and the turbine rotor so as to prevent or reduceleakage therebetween. Typically, the BOAS is mounted in the casing byway a bolted flange on the inner periphery of the casing. The purpose ofthe bolted flange is to accurately and reliably locate the BOAS and toprovide effective sealing against the leakage of BOAS cooling air whichis circulated on the radially outer side of the BOAS to cool and purgethe BOAS.

Such a bolted flange assembly is relatively heavy, and ongoing effortsto reduce the weight of a jet engine favor the elimination of such abolted flange. If the bolted flange is eliminated, however, analternative approach to securing the BOAS in place, and for sealingagainst the leakage of cooling air, must be provided.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, provision is made forlocating and securing the BOAS of a jet engine turbine rotor without theuse of a bolted flange in the engine casing.

By another aspect of the invention, the inner periphery of the enginecasing is so shaped and includes both radially and axially extendingflanges which matingly receive a specially designed locking andretention assembly, which fixes the BOAS in its installed position andalso provides for sealing of its rear periphery.

By yet another aspect of the invention, the sealing and retentionassembly includes a plurality of annular segments that are angle-shapedin cross section with one arm of the angle-shaped segment axiallyengaging a portion of the BOAS and the other arm being so disposed andengaged with the flanges of the casing as to allow the angle-shapedsegment to be rotated about a fulcrum, and by such movement causing asurface of the angle-shaped segment to conformingly engage a matingsurface on the casing so as to thereby provide a sealing function whilepositioning the BOAS.

In the drawings as hereinafter described, a preferred embodiment isdepicted; however, various other modifications and alternateconstructions can be made thereto without departing from the true spiritand scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side elevation sectional view illustrating the bladeouter seal assembly in accordance with the present invention.

FIG. 2 is a perspective view of a radial segment thereof as shown fromthe inner side.

FIG. 3 is a perspective view of a radial segment thereof as shown fromthe outer side.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an annular outer air seal assembly is showngenerally at 10 as applied to an inner surface of a turbine casing 11.As an integral part of the inner surface 12 there is a circumferentiallydisposed mounting flange 13 having a radially inwardly extending leg 14and an axially extending leg 16. The mounting flange 13 forms acircumferential groove 17 between an inner surface 18 of the turbinecasing 11 and an outer surface 19 of the axially extending leg 16. Alsoformed on the inner side of the turbine casing 11 are thecircumferential slots 21 and 22.

The above described structure within the turbine casing is adapted tosupport a blade outer air seal (BOAS) shown at 23 in FIG. 1. As will beseen in FIGS. 1-3, the BOAS comprises a plurality of circumferentiallyspaced, interconnected segments 24 having a generally axially extendingseal portion 26, a plurality of radially disposed arms 27 (See FIG. 1)and a plurality of hanger elements 28. The arms 27 are hidden in FIG. 3but are shown in FIG. 1, whereas the hanger elements 28 are hidden inFIG. 1, but shown in FIG. 3. The hanger elements 28 fit into thecircumferential groove 17 and are supported by the axially extending leg16.

As shown in FIG. 3, in addition to the arms 27 and hanger elements 28,the BOAS segments 24 have other support elements 29 disposed towardtheir upstream end which are mounted in appropriate structure on theinner side of the turbine casing 11 but not shown in FIG. 1.

Although the axially extending leg 16, in cooperation with the hangerelements 28, acts to position and support the BOAS segments 24 in theradial direction, it is also necessary to locate and fix these sealelements in the axial direction. This is accomplished by the use of anangle-shaped seal 31 and a split retention ring 32. The angle-shapedseal 31 is dual purpose in that it provides, in conjunction with thesplit retention ring 32, a physical locating device for the BOAS, aswell as providing sealing for the higher pressure air outboard of theBOAS which is used to cool and purge the BOAS.

Referring again to FIG. 1 and FIG. 3, the angle-shaped 31 seal comprisesa radially disposed arcuate-shaped panel 33 with a plurality of axiallyextending hooks 34. As shown in FIG. 3, the hooks 34 fitcircumferentially between the hanger elements 28 of the BOAS, with bothbeing disposed within the groove 17 as shown in FIG. 1. For purposes ofassembly, the BOAS segments 24 are first assembled from the rear of theengine, with the hanger elements 28 sliding into the circumferentialgroove 17, and then the multiple arc-shaped angle-shaped seal segments31 are slid behind and hook into the same groove 17 to either side ofthe BOAS hanger elements 28.

Also projecting from the radially disposed arcuate-shaped panels 33 arethe forwardly extending flanges 36 and the rearwardly extending flanges37. The ends of the forwardly extending flanges 36 fit into slots 38 onthe rear side of the arm elements 27 as shown in FIG. 1. It is theseforwardly extending flanges 36 which bear against the slots 38 to holdthe BOAS in its axial position. The retention ring 32 then interactswith the rearwardly extending flange 37 and the circumferential slot 32to lock the assembly in its position. The details of how this occurs isfully described in U.S. patent application Ser. No.: (Docket No.:1235_(—)015) filed concurrently herewith and incorporated herein byreference.

In addition to the function of the forwardly extending flange 36 actingto bias the BOAS forwardly, an advantage is taken of the tendency forthe BOAS arm element 27 to be rotated as the BOAS is biased rearwardlybecause of the pressure differential across the BOAS, to aid in thesealing function. That is, as the BOAS is moved rearwardly against theforwardly extending flange 36, the angle-shaped seal 37 is rotated aboutthe fulcrum that exists between the leg outer surface 19 and a pad 39 onthe axially extending hook 34. With the rotation of the angle-shapedseal, a radially outer surface 41 of the arcuate-shaped panel 33 isbiased against the inner surface 18 of the casing 11 to provide asealing relationship that prevents the leakage of cooling airrearwardly. Thus, with the engagement of these two surfaces and those ofthe forwardly extending flanges 36 in the slot 38, a seal is created toprevent the rearward flow of the cooling air.

One of the noteworthy concepts of the above described design is therelatively long axially extending hooks 34. Due to tolerance stack up,other retention schemes considered would not provide any consistentaxial stop location for the BOAS. For example, a radial segment fittinginto the case but extending inwardly enough to provide the seal couldhave an axial position tolerance of 0.002 inches with the case slot.With the long arm, this distance could translate into a substantialamplification of the tolerance on the piece, allowing the BOAS to slideaft by a significantly greater amount. With the current design however,any aft motion of the BOAS produces a tilt on the angle-shaped seal.With a similar 0.002 inch tolerance on the axially positioning of theaxially extending hooks 34, the BOAS can slide aft by no more than 0.002inches. Accordingly, tight control of the tolerance in the radialdistance between the casing inner surface 18 and the axially extendingleg outer surface 19 is critical to ensure a consistent preload of theL-seal. Further, the effect of segment to segment variations in partlength is also minimized with this design.

In addition to the length of the axially extending hooks 34, the radialheight of the panel 33 is important. This radial height is preferablyset to provide a sealing surface against the inboard portion of the BOASand for ease of assembly.

Referring now to FIG. 4, there are a pair of adjacent angle-shapedsegments 31 and, as will be seen, there is a gap 42 that exists bothbetween the adjacent axially extending hooks 34 and between the adjacentarcuate-shaped panels 33. With respect to the gap between the adjacentarcuate-shaped panels 33, leakage of cooling air can occur therebetween,and therefore it is necessary to seal this gap. This is accomplished byway of a shiplap arrangement that is obtained by attaching small plates43 that cover the gap 42 and extend in overlapping relationship over theadjacent arcuate-shaped panels 33. The plates 43 are preferably attachedby welding or the like. Alternatively, the plates 43 could be producedby machining them from the solid segments.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail may be effected therein without departing from the spirit andscope of the invention as defined by the claims.

1. Apparatus for securing an outer seal assembly of a turbine rotorstage to a turbine casing comprising: a plurality of radially outwardlyextending arms on said outer seal assembly, said arms having a rearsurface and a plurality of axially forwardly extending hanger elements;a mounting flange formed on the inner side of said casing and having aradially inwardly extending leg and an axially rearwardly extending legwith a radially outer surface which, together with the inner side ofsaid casing, forms a circumferential groove for receiving said hangerelements therein; a plurality of arcuate elements having an angle-shapedcross section and comprising a radially extending panel with a pluralityof axially forwardly extending hooks adapted to be received in saidcircumferential groove and having at least one axially forwardlyextending flange for engaging said arm rear surface of said outer sealassembly; and a lock for locking said outer seal assembly andangle-shaped flange in their installed positions within said grooves. 2.Apparatus as set forth in claim 1 and further wherein said outer sealassembly arm rear surface includes at least one slot for receiving saidaxially forwardly extending flange.
 3. Apparatus as set forth in claim 1wherein said arcuate elements further include an axially rearwardlyextending flange for engaging with said locking means.
 4. Apparatus asset forth in claim and further wherein said arcuate elements include aradially outer edge which engages an inner surface of said casing in asealing relationship.
 5. Apparatus as set forth in claim 4 wherein, whensaid outer seal assembly arm rear surface is urged rearwardly againstsaid forwardly extending flange of said arcuate element, the arcuateelement is rotated in a counterclockwise direction with the radiallyouter surface of said rearwardly extending leg acting as a fulcrum,thereby resulting in the radially outer edge of said arcuate elementbeing biased against said casing inner surface.
 6. Apparatus as setforth in claim 5 wherein said axially forwardly extending hooks of saidarcuate elements include a pad for engaging said axially rearwardlyextending leg to thereby facilitate the rotational movement. 7.Apparatus for locking a blade outer air seal (BOAS) in place about aturbine rotor stage for a jet engine that includes: an engine casingthat surrounds said rotor stage, said casing having a circular radiallydisposed wall and an axially disposed groove adjacent said wall, saidgroove having an inner wall and an outer wall, said outer wall extendingoutwardly beyond the entrance to said groove; an annular hanger forsupporting the BOAS, said hanger having a plurality of circumferentiallyspaced hanger elements that extend into said groove, said hanger furtherhaving a front face that is adjacent to the radial wall of the casingand an opposing rear face; an annular segmented assembly wherein eachsegment includes an arcuate shaped radially disposed panel and aplurality of hooks attached to said panel and passing between the hangerelements into said groove, each panel having a first sealing padextending along its radially outer rim that rests in sealing contactagainst the outer wall of said groove and a second sealing pad extendingalong the front face of the panel that rests in sealing contact againstthe rear face of the annular hanger; each hook having a contact portionwhich engages said groove inner wall which acts as a fulcrum to apply atorque to the associated panel through said lever arm; and means toprevent axial movement of said segmented assembly.
 8. Apparatus as setforth in claim 7 and further wherein said hanger rear face includes atleast one slot for receiving said second sealing pad.
 9. Apparatus asset forth in claim 7 wherein said arcuate shaped radially disposed panelfurther includes a rearwardly extending flange for engagement with saidmeans for preventing axial movement.
 10. A method for securing an outerseal assembly of a turbine rotor stage to the turbine casing comprisingthe steps of: providing a plurality of radially outwardly extending armson said outer seal assembly, said arms having a rear surface and aplurality of axially forwardly extending hanger elements; providing amounting flange on the inner side of said casing and having a radiallyinwardly extending leg and an axially rearwardly extending leg with aradially outer surface which, together with the inner side of saidcasing, forms a circumferential groove for receiving said hangerelements therein; providing a plurality of arcuate elements having anangle-shaped cross section comprising a radially extending panel with aplurality of axially forward extending hooks adapted to be received insaid circumferential groove and having at least one axially forwardlyextending flange for engaging said arm rear surface of said outer sealassembly; and locking said outer seal assembly and said angle-shapedflange in their installed positions within said groove.
 11. A method asset forth in claim 10 and including the step of providing a radiallyouter edge on said arcuate element, with said radially outer edgeengaging an inner surface of said casing in a sealing relationship. 12.A method as set forth in claim 10 wherein said locking step isaccomplished with a locking mechanism disposed near the radially outerportion of said arcuate element such that, when the arm rear surface isurged against the axially forwardly extending flange of said arcuateelements, the arcuate element is allowed to rotate so as to thereby biassaid radially outer edge against said casing inner surface.